The present invention relates to manufacture of a semiconductor device, and more particularly, to an electron beam (e-beam) exposure apparatus for irradiating an e-beam to a resist to draw patterns.
A lithography process is carried out to realize a semiconductor device on a wafer. In the lithography process, a layout of circuit patterns for forming a semiconductor device is first designed and a process for fabricating a photomask is then carried out by forming a mask pattern according to the designed pattern layout onto a transparent quartz substrate. After that, an exposure process using the photomask is carried out on a photoresist layer on a wafer with an exposure apparatus, thereby realizing a photoresist pattern according to the designed layout on the wafer. By carrying out a selective etch process using this photoresist pattern, a circuit pattern is actually formed on the wafer.
In order to pattern transfer the designed pattern layout onto the mask pattern during the process of fabricating the photomask, a resist drawing or exposure process using an e-beam exposure apparatus is carried out. For example, a chrome (Cr) layer or a molybdenum (Mo) alloy layer is formed as a mask layer on the transparent quartz substrate, a resist layer is coated on the mask layer and e-beam is then scanned using the e-beam exposure apparatus, thereby carrying out a selective exposure on the resist layer.
A resist pattern is formed by developing the e-beam exposed resist layer and the mask pattern is formed by carrying out a selective etch process using the resist pattern. Therefore, uniformity of a Critical Dimension (CD) of the mask pattern depends on the uniformity of the CD of the resist pattern used as an etch mask. The uniformity of the CD of the resist pattern largely depends on an exposure accuracy upon actual e-beam exposure or an exposure precision of the e-beam exposure apparatus.
As one of factors that influence on the uniformity of the CD of the resist pattern, a fogging effect by electron scattering below an e-beam column part having a magnetic lens and beam slots may be considered. e-beam incident to the surface of the resist layer may result in electrons rebounding from the surface, for example, forward scattered electrons.
Since the e-beam irradiated from the e-beam exposure apparatus is in an accelerated state with a constant acceleration voltage, relatively many electrons rebound from the surface of the resist layer into a region of high open ratio, i.e. a portion having a large area to be actually exposed. These electrons are scattered on the resist layer and may enter into the resist layer. Therefore, the area to be exposed in the resist layer may not be precisely removed and this may result in an enlarged pattern size that is over CD.
When this fogging effect results, the uniformity of the CD of the resist pattern is lowered, and accordingly, the uniformity of the CD of the mask pattern etched according to the CD of the resist pattern may also be lowered. This lowering in the uniformity of the CD of the mask pattern consequently results in lowering in uniformity of the CD of the wafer pattern formed by pattern transfer of the mask pattern onto the wafer. A solution that can reduce or inhibit the fogging effect during the e-beam exposure is beneficial.